1. Field of the Invention
This invention relates generally to thermal inkjet printing. More particularly, this invention relates to an economical, low-cost thermal inkjet printer having a path for print media (e.g., paper or plastic printing film) advancement, and which defines a media advance direction. The printer also includes an inkjet printing cartridge. During a printing interval the inkjet printing cartridge controllably ejects droplets of printing fluid (i.e., ink, for example) onto the print media from a generally linear array of printing orifices. During this printing interval the printing cartridge is controllably moved in a direction parallel with the media advance direction and generally perpendicular to the length of the linear array of printing orifices in order to print in a xe2x80x9cswathxe2x80x9d on the media. Between printing intervals, the print media may be advanced in step-wise fashion along the media advancement path, or the printing cartridge may be shifted laterally of the media advance direction, or stepped among plural printing positions for the printing cartridge, or both.
2. Related Technology
One form of conventional thermal inkjet printer or plotter typically has a print cartridge mounted on a movable carriage. This carriage is traversed back and forth across the width of a print media (i.e., usually paper or a plastic plotting film, for example) as the print media is fed through the printer or plotter. Plural orifices on a print head of the print cartridge are fed ink (or other printing fluid) by one or more channels communicating from a reservoir of the print cartridge. Energy applied individually to addressable resistors (or to other energy-dissipating elements, for example, to piezoelectric actuators), transfers energy to ink or other printing fluid at the print head; which ink (printing fluid other than ink hereinafter being subsumed also in the term xe2x80x9cinkxe2x80x9d) is within or associated with selected ones of the plural orifices. These orifices then eject a part of the ink onto the printing media. The ejected ink forms a fine-dimension jet or stream that impinges on the printing media at a selected location dependent upon the relative positions of the print media and of the selected orifice(s) from which ink is ejected.
Another form of conventional thermal inkjet printer has a media transport mechanism that controllably moves print media past an array of plural print cartridges, each with a respective print head. In this type of inkjet printer, the print cartridges are arrayed in a stationary array, usually of xe2x80x9cblock wallxe2x80x9d arrangement, or in a diagonally arrayed and slightly overlapped arrangement, so that the entire width of the print media (or of that portion of the print media on which printing is to be done) passes by the print heads as the media is controllably moved through the printer.
With each type of conventional thermal inkjet printer mentioned above, the print media transport mechanism must be able to move and position the print media with high precision. The first type of conventional thermal inkjet printer or plotter must also have a highly precise mechanism for moving the carriage carrying the inkjet print cartridge relative to the print media. In each case, the resolution or precision of the characters or images produced by the printer is highly dependent upon the precision of the print media advance mechanism, and possibly also on the precision of the print cartridge scanning mechanism. For this reason, printers of these conventional types have had a relatively high cost.
However, there are several thermal inkjet printing applications in which high resolution or precision of images and characters are of secondary importance. Such applications include the printing of retail transaction receipts, the printing of credit card and debit card transaction receipts, and the printing of ATM machine receipts, for example. In each case, the document or receipt printed is strictly a utility document, and will likely have a short useful life. In many cases the recipient of the printed document merely glances at it to confirm a transaction just completed, and then immediately discards the paper document. In other cases, the receipt or transaction record documents are kept only until a monthly statement is received from the credit card company. Thus, after the transaction receipts and monthly statement are compared, the receipts are all discarded. In such high-volume printing applications, a low cost and high speed of production for the printed document is of far greater importance that is the precision or resolution of the printing on the document. While such documents must be legible, high quality printing and image presentation is not required.
Despite the above, it is common in conventional printers for printing such low-resolution documents and receipts to employ of printer of the first type described above. That is, the printer includes a print cartridge mounted on a movable carriage. This carriage is traversed back and forth across the width of a print media, which may be a comparatively narrow strip of paper still attached to a roll of paper as the paper is fed through the printer or plotter, for example. Relatively high precision is required for both the traverse mechanism carrying the print cartridge and for the paper feed mechanism. Further, and especially because of the comparatively narrow width of the paper strip on which a receipt or other such document is being printed, the traverse mechanism for the printing cartridge makes many scans back and forth across the narrow width of the document as the paper is advanced. In this way, the speed of the printer is kept at a slow pace because so much time is spent in stopping and starting the print cartridge at the ends of these plural scans across the narrow paper strip.
It would be an advantage if a thermal inkjet printer could be provided that reduced or eliminated the many scans of a print cartridge back and forth across a narrow print media strip, such as a receipt strip cut from a roll of paper.
It also would be an advantage if a thermal inkjet printer could be provided that did not require precise movements of the print media advance mechanism. That is, if print media could be advanced in a step-wise motion by a low-precision stepping mechanism then such a thermal inkjet printer could be provided to the public at a much reduced cost.
In view of the deficiencies of the related technology, an object for this invention is to reduce or overcome one or more of these deficiencies.
The present invention provides a thermal inkjet printer could be provided that reduced or eliminated the many scans of a print cartridge back and forth across a narrow print media strip.
According to one aspect, the present invention provides a thermal inkjet printer in which a print cartridge is scanned lengthwise of an elongate strip of print media, in the same direction as print media advance, and all printing by the cartridge is accomplished during a printing interval with the print media stationary and the print cartridge progressing lengthwise of the print media.
According to another aspect of the present invention, such a thermal inkjet printer provides for printing a document having a width which is greater than the print head of the print cartridge by stepping the print cartridge laterally between printing intervals by a distance about equal to the print head width. In a next-subsequent printing interval, the print cartridge again progresses lengthwise of the print media to accomplish printing.
The present invention also provides a thermal inkjet printer that does not require precise movements of the print media advance mechanism.
Further to the above, the present invention provides such a thermal inkjet printer in which the print media is advanced in step-wise fashion between printing intervals, and is advanced by a unit length in the direction of the paper length (i.e., in the direction of the length of paper from a roll, for example). During printing intervals, the paper is stationary, and the paper advancing mechanism may operate with a relatively low precision.
According to one embodiment, the present invention provides a thermal inkjet printer comprising a housing defining a print media transport path defining a print media transport direction and having an exit; a print media transporter controllably moving a planar flexible print media in the transport direction from a supply thereof along the print media transport path and to the exit; an inkjet printing cartridge having an array of plural fine-dimension printing orifices, the inkjet printing cartridge during a printing interval controllably ejecting droplets of printing fluid from selected ones of the plural printing orifices and onto the print media; and carriage means controllably moving the printing cartridge in a direction substantially parallel to the print media transport direction and closely spaced to the print media.
According to another aspect, this invention provides a method of printing on elongate planar flexible media, the method comprising steps of: transporting print media unidirectionally along a path in a media transport direction; moving a inkjet printing cartridge proximate to the print media in a direction substantially parallel with the print media transport direction; and during movement of the printing cartridge relative to the print media controllably ejecting droplets of printing fluid from the printing cartridge and onto the print media.
Other objects, features, and advantages of the present invention will be apparent to those skilled in the pertinent arts from a consideration of the following detailed description of a single preferred exemplary embodiment of the invention, when taken in conjunction with the appended drawing figures, which will first be described briefly.